Engine-powered astrophysical transients
Recent surveys have revealed various previously unknown types of supernova-like transients, challenging our understanding of how massive stars end their lives. Among those are the unusually energetic explosions, dubbed superluminous supernovae (SLSNe), which outshine their more ordinary counterparts by a few orders of magnitude. Established radioactively-powered supernova models fail to explain their prodigious luminosities, requiring a different mechanism. I will discuss the concept of a central engine -- an embedded persistent energy source that continues to deposit power into the supernova ejecta well after the initial explosion. A rapidly spinning newborn highly magnetized neutron star (a magnetar) constitutes a promising candidate for such an engine in a significant fraction of SLSNe. I will discuss in some detail the radiative modelling and multiwavelength signatures expected from magnetar-powered supernovae, as well as potential applications to other kinds of explosive events. The latter includes multimessenger transients like GW170817, a gravitational wave event from a double neutron star merger, simultaneously detected across the electromagnetic spectrum from radio frequencies to gamma rays.